Solid wood floor - underlay?

[AdamD]

Which underlay for solid oak on both concrete and timber floor boards above suspended floor?

[Nickfromwales]

You'll need to work out if there's need for moisture control and where you're integrating that. For the timber floors I doubt you'll need any underlay, but some insulation may be of benefit.

 

Can you provide some more details of what's there / what you propose?